It is known to provide circulation subassemblies (circsubs) in drill pipes in the oil and gas industry. Such circsubs allow drilling fluid that is pumped down the drill pipe to bypass the bottom hole assembly (BHA) by providing an opening that can selectively allow fluid communication between the bore of the drill pipe and the annulus between the drill pipe and the well bore. This may be useful if an operator wishes to clean part of the annulus with drilling fluid at high flow rate. It may also be useful for introducing lost circulation material (LCM) to seal the well bore and prevent loss of drilling fluid. It is undesirable to introduce LCM around the BHA, as this may cause the BHA to become stuck.
Known circsubs may be actuated by a variety of different methods, including by passing a dart or a ball down the bore of the drill pipe. However, this method has the disadvantage that the darts or balls can often only be passed down the bore of the drill string when drilling fluid is able to flow down the drill pipe.
Some circsubs only allow partial bypass of the BHA. That is, they selectively allow or prevent fluid communication between the bore of the drill pipe and the annulus between the drill pipe and the well bore, but they cannot prevent fluid communication between the bore of the drill pipe above the circsub and the BHA. It is desirable to provide the possibility of both full bypass in which fluid communication between the bore of the drill pipe and the BHA is prevented but fluid communication between the bore of the drill pipe and the annulus is allowed and partial bypass. However, this increases complexity.
A known circsub, which is available from Drilling Systems International (DSI) under the trade name PBL® Sub, is operable to provide full bypass of a BHA. It is placed in the full bypass condition by passing a vinyl ball down the bore of the drill pipe. The tool can be returned to the flow through condition by inserting deactivation balls to block the bypass holes and increasing the pressure to a predetermined value, which causes the vinyl ball to shear and move through the circsub to a catcher assembly. The deactivation balls also move through the circsub to the catcher assembly. A disadvantage of this arrangement is that transitions between conditions can only be made when drilling fluid is able to flow through the circsub, and the number of transitions that are possible before the circsub must be removed from the well bore is limited by the space available to store used balls.
The present invention seeks to at least partially mitigate the problems identified with the prior art.